High-pressure chamber

ABSTRACT

A high-pressure chamber having an inner tubular member circumscribed by a concentric outer tubular member of fully autofrettaged fabrication with a segmented circumferentially complete cylinder of high compressive strength material extending between the inner and outer tubular members.

United States Patent Inventors Victor C. D. Dawson [56] References Cited illverl'dspErlggj I Ch UNITED STATES PATENTS A 1 No :32 1,521,717 1/1925 Schmidt 29/1.1 27 1968 2,218,669 10/1940 Whipple..... 83/High Pressure Digest Patented Maw 3,376,624 4/1968 Eves 2 9/1.1 841,972 1/1907 Huber ..l8/High Pressure Digest Assgnee g f ggzig fiz zg fli "presented 1,782,103 1 1/1930 Solberg et a1. .18/High Pressure Digest y l y 2,218,660 10/1940 Whipple ..18/High Pressure Digest 2,554,499 5/1951 Poulter ..18/High Pressure Digest Primary Examiner-Andrew R. J uhasz Assistant Examiner-Leon Gilden Att0meysS. P. Fisher, R. S. Sciascia and J. A. Cooke HIGH-PRESSURE CHAMBER 3 Claims 2 Drawmg Flgs' ABSTRACT: A high-pressure chamber having an inner tubu- U.S.Cl 18/165, lar member circumscribed by a concentric outer tubular l8/(Digest) 26 member of fully autofrettaged fabrication with a segmented Int. Cl B29c 3/00 circumferentially complete cylinder of high compressive Field of Search 18/ l 6.5 strength material extending between the inner and outer tubu- (High Pressure Digest); 29/ 1 .1 lar members.

X 22 46' I\ I? x HIGH-PRESSURE CHAMBER BACKGROUND OF THE INVENTION This invention relates generally to pressure chambers and more particularly to a pressure chamber capable of withstanding very high pressures.

Technological developments have demanded an ever increasing need for vessels capable of containing very high pressures, for example in experimental work, in the manufacture of gun barrels, and in the production of synthetic gems. The pressure capability of cylindrical vessels has in the past been limited to values of about 200,000 pounds per square inch. Where pressures higher then these have been obtained, either very small size vessels were involved or the pressures achieved were transient. Numerous chambers have been designed with a capability of containing pressures as high as 500,000 pounds per square inch, but, in general, these have been of an elaborate design, generally confined to small sizes, and limited to very select applications.

A cylindrical monobloc vessel has been utilized in the past, but this structure has been limited in its elastic pressure containment capability since the strength of the material from which the vessel can be constructed is limited and the cylindrical geometry is such that high nonuniform stresses of both tension and compression are induced at the bore of the vessel by inner pressurization resulting in yielding at the bore. The limitations on a monobloc vessel are illustrated by the following equation which relates the yield pressure Py to the yield strength Y, of the material and the wall ratio at of the cylinder:

where Py is the internal pressure which would just initiate yielding at the inner bore of the cylinder. Thus, a monobloc cylinder with an infinite wall ratio, a) would only have an elastic pressure capability of Since the yield strengths of high strength steels, at least in large sections, are limited to about 200,000 p.s.i., the maximum pressure that can be maintained without yielding is approximately 1 15,000 p.s.i.

An examination of the stress distribution in a cylinder at the instant it reaches the yield conditions indicates that even though the bore stresses are high, the stresses progressively decrease through the wall and at the outer surface reach relatively low values. Furthermore, the application of an external pressure to a cylinder will induce a negative compressive hoop stress at the bore. This negative hoop stress can reach quite high values for comparatively low pressures externally applied. This phenomenon has resulted in a proposal of a chamber constructed of two or more concentric cylinders in which the outer cylinder, i.e., jacket is shrunk onto the inner cylinder, i.e., liner. This is a conventional technique that is used to increase the elastic operating pressure range of a vessel. The shrink-fit generates an interference pressure between the liner and jacket which creates negative hoop stresses at the bore of the liner and positive hoop stresses at the bore of the jacket. When internal pressure is subsequently applied to the bore of the liner, it does not create a positive hoop stress until a pressure high enough to the shrink-fit construction is reached. Even though initially the jacket in this situation has a positive hoop stress, the nonuniformity of the stress caused by the internal pressure is such that, under proper design conditions, the combined stress of the bore of the jacket will remain below the yield condition. The shrink-fit construction, although better than a monobloc construction, does have limitations. The major limitation is that there is a limit to the negative stress that can be induced in the bore of the liner (when the stress condition at the bore of the liner reaches the yield point in compression). Thus, the

overcome a negative hoop stress of maximum attainable elastic pressure capability for a shrink-fit construction is twice the value for a monobloc construction. This maximum value can only be realized by using a large number of concentric cylinders shrunk together, or by using a small number of cylinders, each having a large wall ration.

The principle of the shrink-fit is to create initially compressive hoop stresses at the bore of the cylinder. Such compressive hoop stresses can also be created by the prior art process of autofrettage during chamber manufacture. In this process the cylinder is subjected to a sufficiently high value of internal pressure to cause yielding through all, or part, of the cylinder wall. After the pressure is released, residual stresses exist in the cylinder wall and the inner bore is left with a residual compressive hoop stress. Hence, because of this stress, the autofrettaged cylinder is, as was the case of the shrink-fit, capable of operating elastically at a higher internal pressure. If a monobloc cylinder is pressurized during manufacture to magnitudes greater than that given for the yield pressure but no more than the pressure required to yield the cylinder through the entire wall, it will be found that residual compressive stresses exist at the bore so that the situation similar to that of shrink-fit construction occurs. Again, however, there are limitations. For example, if the residual stresses become high enough, yielding in compression will occur at the bore. This phenomenom is known as reverse yielding. If it is desired to have an elastic pressure capability, the autofrettage pressure must be limited to values just below the pressure that will cause reverse yielding. For wall ratios less than 2.22, a cylinder can be pressurized to the pressure required to yield the cylinder through the entire wall without having reverse yielding occur when the present is released. For wall ratios greater than 2.22 the autofrettage pressure is limited to twice the value of the yield pressure of a monobloc cylinder if reverse yielding is to be prevented. Within these limits the autofrettage pressure represents the operating pressure capability of a cylinder.

All of the prior art pressure vessels have been limited in their maximum pressure capability to approximately 200,000 pounds per square inch with the exception of very elaborately designed pressure vessels of extremely small size which have exhibited capabilities as high as 500,000 p.s.i.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is to provide a new and improved chamber capable of withstanding very high internal pressures.

Another object of the invention is the provision of a new and improved chamber of relatively large internal dimensions capable of withstanding very high internal pressure.

One other object of this invention is the provision of a new and improved chamber of relatively large internal dimension capable of withstanding internal pressures as high as 1 ,000,000 p.s.i. without yielding in the wall structure.

Briefly, in accordance with one embodiment of this invention these and other objects are attained by providing a highpressure chamber having a first cylindrical tubular member, a second cylindrical tubular member of fully autofrettaged high strength fabrication concentric with and circumscribing the first tubular member, a segmented cylinder made up of a ring of block members between the first and second tubular members, and means for enclosing the first tubular member.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the attendant advantages thereof will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a longitudinal sectional view of the pressure chamber of the present invention; and

FIG. 2 is a transverse sectional view taken along the line 2-2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein like reference characters designate identical or corresponding parts throughout the several views, and more particularly to FIG. I thereof wherein the high-pressure chamber of the present invention is shown as consisting essentially of a first cylindrical tubular member 10, a second cylindrical tubular member 12 concentric with and circumscribing the first tubular member 10,-and an axially segmented cylindrical member 14 extending between the first and second tubular members. Tubular member 12 is fabricated of fully autofrettaged high strength material such as steel. Piston-type plug members 16 and 18 are provided for enclosing the ends of the first tubular member 10. Tubular member is supported by integrally formed enlarged cylindrically shaped end members 20 each of which has defined in the outer faces 22 thereof a conical opening 24 which is in communication with a cavity 26 formed in member 10 for containing a medium under high pressure. The piston-type plug members 16 and 18 each have a conical wall surface 28 of a configuration conforming to the conical opening 24, and protruding piston sections 30 and 31 extending within the pressure cavity 26 and having sealing means, such as Carboly rings 32 sealed thereon. A pair of cylindrically shaped end closure plug members 34 and 36 are respectively threadedly mounted in the opposite ends of the tubular member 12 as shown at 38 and 44 for enclosing the ends of the second tubular member 12. The particular means for pressurizing cavity 26 is not part of the present invention, and any conventional pressurizing technique can be utilized. As an example of one conventional pressurizing technique, the pistontype plug 16 would be withdrawn from cavity 26 until surface 44 on piston 16 comes into abutment with surface 46 on end block 34 and a high-pressure fluid would be introduced into a cylinder cavity 48 by piping extending through members 34 (not shown) to move piston 16 and extension 30 back into pressure cavity 26. Due to the great differential between the surface areas of face 44 and the face of extension 30 a much higher pressure will result in pressure cavity 26 then that provided to cavity 48.

As shown in FIG. 2, the segmented cylindrical member 14 is made up of a circumferentially complete ring of elongate block members 42. The block members 42 are each fabricated of a very high compressive strength material such as Carboloy or glass. The utilization of the segmented cylindrical member 14 is only advantageouswhen the overall wall ratio of the pressure vessel (the outside diameter of the second cylindrical tubular member divided by the inside diameter of the first cylindrical tubular member) is greater than 2.22.

' If the jacket wall ratio (the outside diameter of the second v. tubular member divided by the inside diameter of the second cylindrical tubular member) is less than 2.22 the maximum autofrettage pressure is For a jacket wall ratio greater than 2.22 the maximum autofrettage pressure for elastic operation is P= Y In to for w$2.22

chamber construction, the optimum jacket wall ratio is 2.22. To autofrettage a cylinder with this wall ratio requires a pres- P for Q2 2.22

Since where P,- is the pressure applied to the pressure cavity 26 and a), the ratio of the outside diameter of the segmented cylinder to the internal diameter of the pressure cavity, the internal pressure capability is 0.92Yuw 2.22

The elastic pressure capability of a segmented chamber with an autofrettaged jacket is higher than that of any of the other systems considered and, in fact, exceeds the burst strength of a monobloc cylinder for wall ratios greater than about 3.5.

The present invention utilizing a segmented cylindrical chamber design having a fully autofrettage outer jacket with an overall wall ratio of the pressure vessel greater than 2.22 and an optimum jacket wall ratio equal to 2.22 provides a high-pressure chamber capable of withstanding pressures of considerably greater magnitude than any design previously proposed.

Obviously, numerous modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

We claim:

1. A high-pressure chamber comprising a first cylindrical tubular member having an inside and outside diameter,

a second cylindrical tubular member of fully autofrettaged high strength fabrication concentric with and circumscribing said first tubular member and having an inside and outside diameter, said outside diameter of said second tubular member being greater than 2.22 times said inside diameter of said first tubular member, multiplicity of block members defining a segmented cylinder between said first and'second tubular members, and

means for enclosing said first tubular member.

2. The high-pressure chamber of claim 1 wherein the outside diameter of said second tubular member is 2.22 times said inside diameter of said second tubular member.

3. The high-pressure chamber of claim 2 wherein said block members are fabricated of a high compressive strength material. 

1. A high-pressure chamber comprising a first cylindrical tubular member having an inside and outside diameter, a second cylindrical tubular member of fully autofrettaged high strength fabrication concentric with and circumscribing said first tubular member and having an inside and outside diameter, said outside diameter of said second tubular member being greater than 2.22 times said inside diameter of said first tubular member, a multiplicity of block members defining a segmented cylinder between said first and second tubular members, and means for enclosing said first tubular member.
 2. The high-pressure chamber of claim 1 wherein the outside diameter of said second tubular member is 2.22 times said inside diameter of said second tubular member.
 3. The high-pressure chamber of claim 2 wherein said block members are fabricated of a high compressive strength material. 